It is our objective to carry out detailed structure analyses of enzymes by the established technqiues of x-ray crystallography. We propose to continue studies of flavoproteins, already initiated by solution of the structures of flavodoxins from Clostridium MP and A. nidulans. The conformation of the latter flavodoxin will be refined and studied as a function of oxidation state. Analyses of flavoproteins will be extended to lactate oxidase and to complexes of electron carriers with feredoxin-NADP-reductase. The preliminary model of the conformation of cytochrome c557 from A. nidulans will be improved by phasing to a resolution of at least 2.5A. Additional heavy atom derivatives of crystalline Fe- and Mn- superoxide dismutases will be sought in order to determine these structures by isomorphous replacement.